1. Field of the Invention
The invention relates to a driving technique of a fluorescent lamp, more particularly, to an apparatus for driving a fluorescent lamp without using a boost transformer.
2. Description of the Related Art
Fluorescent lamps (for example, cold cathode fluorescent lamps (CCFLs)) are widely applied to the backlight systems in monitors and televisions of large-scale liquid crystal displays (LCDs). As shown in FIG. 1, an apparatus 10 used for driving a CCFL CL generally includes a power switching circuit 101, a boost transformer T, and a resonator formed by a leakage inductance of the boost transformer T and two capacitors C.
Generally, the power switching circuit 101 is coupled between an input voltage VDD (which is a direct current (DC) voltage of about 380V) and a ground potential GND, and is used for switching and outputting the input voltage VDD and the ground potential GND in response to a ramp signal RMP with fixed frequency and a comparison voltage CMP, so as to generate a square signal SQ. Moreover, the resonator formed by the leakage inductance of the boost transformer T and the two capacitors C filters/converts the square signal SQ generated by the power switching circuit 101 to generate a sinusoidal driving signal SIN (which has a root mean square (RMS) value of about 342V) for driving the CCFL CL.
However, since the CCFL CL requires a relative high operation voltage with an RMS value of about 700V, the boost transformer T has to be used to boost the sinusoidal driving signal SIN to a voltage range capable of operating the CCFL CL. Therefore, the apparatus 10 used for driving the CCFL CL has to use the boost transformer T, or otherwise the CCFL CL cannot be successfully driven.